Is when an object experiences only one force--Gravitational pull.
This means free fall only truly occurs in a...
Vacuum
Where there is no air resistance (because in a vacuum, there is no air).
This causes the object to have a constant acceleration of
9.81 ms^-2 (Earth's gravitational acceleration).
Because there is no air resistance, all objects will fall with the
uniform acceleration of 9.81 ms^-2, and reach the ground at the
same time.
This is regardless of their size, mass, surface area, etc.
Example for you to picture in your head: In a vacuum, if a feather and a bowling ball were
dropped at the same time, both objects would reach the ground at the same time.
(This is hard to picture but it is proven, there is a video on this.)
https://www.youtube.com/watch?v=E43-CfukEgs
Nota:
Note to self: the video is in your physics folder in your computer
Without a vacuum, a heavier object would fall
to the ground first.
Factors such as mass and surface area (which will affect air
resistance) will affect the speed of the falling object.